I have made a corporation to make my own heavy armored vehicles but they don't show up in my army, I don't know what to do or am I not waiting long enough for them to appear?
From the Corporations page select the Create production tab. You will see your corps and the amount they produce. In the field to the right of the desired corp type in the amount you wish to contract. Scroll to the bottom of the page. The contract to your country should be selected, then click Submit.